1) Field of the Invention
The present invention relates to a photosensitive resin composition having heat resistance, and more particularly to a photosensitive resin composition which can be applied to semiconductor devices and the like as a surface protecting film layer or an interlayer dielectric film layer. The present invention also relates to a process for forming a relief pattern using the composition, and to an electronic component having such a pattern.
2) Description of the Related Art
In the semiconductor industry, inorganic materials have been conventionally used as materials for interlayer dielectric film layers. However, in recent years, organic substances having excellent heat resistance, such as polyimide resins, have come to be used increasingly as the materials for interlayer dielectric film layers, taking the advantage of their properties.
On the other hand, formation of circuit patterns on semiconductor integrated circuits and printed boards is achieved through a cumbersome, wide-ranging process including formation of a resist layer on the surface of a substrate, exposure of predetermined portions thereof, removal of unnecessary portions by, for example, etching, and a cleaning operation for the surface of the substrate. Therefore, if the resist which lies on portions where an insulating material needs to be provided after the formation of patterns by exposure and development can remain as it is and used as an insulating material, the semiconductor fabrication process will be considerably shortened.
Recently, for shortening the semiconductor fabrication process, as resins used as the resist, use of photosensitive polyimides and polybenzoxazoles as constituent resins for use in resists is becoming mainstream since these resins per se can be imparted with photosensitivity and enable easy pattern formation merely by application, exposure, and development.
The conventional photosensitive polyimides are mainly of the negative type in which an organic solvent is used as a developer and the exposed portion is insolubilized. For example, a polyimide produced by a method in which a compound having a photosensitive group is added to an acid functional group of a polyimide precursor or mixed with the polyimide precursor having an acid functional group is used as a negative photosensitive polyimide which creates a contrast by a photocrosslinking reaction. A related technology has been disclosed in Japanese Patent Application Laid-open No. S54-109828.
On the other hand, recently, there has been an increasing demand of development with an alkaline aqueous solution in order to reduce the cost for materials and protect the environment. Conventionally, those photosensitive resins including a naphthoquinonediazide compound as a photosensitive agent and a polybenzoxazole precursor having an acid functional group as a base resin have been proposed as described in Japanese Patent Application No. H1-46862.
In the case of a positive photosensitive polyimide, the polymer has a low molecular weight and further, unlike the negative polyimide, it does not increase in molecular weight by, for example, crosslinking during the processing, so that the relief pattern obtained after the exposure and development may be fused by heating during the curing process. To overcome such a problem, introduction of a crosslinkable group having a C═C double bond into the terminals of the polymer has been proposed as described in Japanese Patent Application Laid-open No. H11-109620 and Japanese Patent application Laid-open No. H11-143070, respectively.
The photosensitive resins including a naphthoquinonediazide compound as a photosensitive agent and a polybenzoxazole precursor having an acid functional group as a base resin are designed laying importance on the development properties, and hence the molecular weight of the polymer is set to a lower level to thereby increase the solubility. However, the polymer having a decreased molecular weight cannot exhibit satisfactory mechanical properties even when it is cured, and thus the conventional photosensitive resin materials lack favorable properties as the resin.
Further, in the above positive photosensitive resin materials, the C═C double bond possibly undergoes polymerization through a dark reaction. For this reason, the resin changes in viscosity with time, thereby lowering the storage stability. Specifically, a problem arises in that it is difficult to maintain initial properties, such as resin properties and application properties, and photosensitivity properties.